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Feb 3 2008 VH- noob question

 
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d_kahane



Joined: 09 Apr 2009
Posts: 4
PostPosted: Sat May 02, 2009 9:34 pm    Post subject: Feb 3 2008 VH- noob question Reply with quote
So- I've progressed to a stopping point w/ a VH puzzle.. and I can of course guess one of the two candidate cells and figure out how to finish through trial and error.. but that just sucks. Normally I'm a results-oriented guy, but process has to count for something!

Image:



Now I know the next step (per puzzle hint) is a 6 in C6R1 (and i tested a 2 there and it fails because of 6's in column 1). And I'm guessing there is an "X-Wing" to explain why... but I have READ about X-Wings but can't seem to grasp it when I look at a puzzle. I was thinking if someone told me specific to a puzzle I was working in the light bulb my finally click.

In step-by-step fashion, can anyone explain the 6 to me?

Thanks, a ton, to anyone who helps me get mentally untangled!
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storm_norm



Joined: 18 Oct 2007
Posts: 1741
PostPosted: Sat May 02, 2009 10:21 pm    Post subject: Reply with quote
the placement of the 6 isn't from a x-wing.
instead its from the xy-wing present in this image
in
r1c2 {2,4}
r3c1 {4,6}
r3c5 {2,6}



the xy-wing says that either the 2 in r1c2 is true,
or
the 2 in r3c5 is true,
no matter which direction through the chain you go.

this eliminates the 2 in r1c6 and places 6 in that cell.
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wapati



Joined: 10 Jun 2008
Posts: 472
Location: Brampton, Ontario, Canada.
PostPosted: Sat May 02, 2009 10:34 pm    Post subject: Reply with quote
Code:
.---------------------.---------------------.---------------------.
| 5      24     2369  | 1      7      26    | 8      2349   234   |
| 39     7      239   | 4      8      5     | 6      239    1     |
| 46     8      1     | 9      26     3     | 7      5      24    |
:---------------------+---------------------+---------------------:
| 34     45     7     | 2      9      14    | 135    8      6     |
| 3469   245    2369  | 8      456    146   | 12359  2349   7     |
| 8      1      269   | 56     3      7     | 259    249    245   |
:---------------------+---------------------+---------------------:
| 2      6      5     | 3      1      9     | 4      7      8     |
| 7      9      4     | 56     256    8     | 235    1      235   |
| 1      3      8     | 7      245    24    | 25     6      9     |
'---------------------'---------------------'---------------------'



There is also a vertical x-wing present that could be done now, or later.

Code:
.---------------------.---------------------.---------------------.
| 5      24     2369  | 1      7      26    | 8      2349   234   |
| 39     7      239   | 4      8      5     | 6      239    1     |
| 46     8      1     | 9      26     3     | 7      5      24    |
:---------------------+---------------------+---------------------:
| 34     45     7     | 2      9      14    | 135    8      6     |
| 3469   245    2369  | 8      456    146   | 12359  2349   7     |
| 8      1      269   |*56     3      7     | 29-5   249   *245   |
:---------------------+---------------------+---------------------:
| 2      6      5     | 3      1      9     | 4      7      8     |
| 7      9      4     |*56     26-5   8     | 23-5   1     *235   |
| 1      3      8     | 7      245    24    | 25     6      9     |
'---------------------'---------------------'---------------------'


Edited to put in the extra candidates that are in the posted markup.

Last edited by wapati on Sun May 03, 2009 2:06 am; edited 2 times in total
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keith



Joined: 19 Sep 2005
Posts: 3355
Location: near Detroit, Michigan, USA
PostPosted: Sat May 02, 2009 10:40 pm    Post subject: Reply with quote
d_kahane,

Get yourself a copy of Sudoku Susser. It explains the reasoning behind the moves.

Keith
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Marty R.



Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA
PostPosted: Sun May 03, 2009 12:32 am    Post subject: Reply with quote
Quote:

There is also a vertical x-wing present that could be done now, or later.


But if one does the XY-Wing, there is no "later."
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d_kahane



Joined: 09 Apr 2009
Posts: 4
PostPosted: Sun May 03, 2009 2:30 pm    Post subject: Reply with quote
storm_norm wrote:
the placement of the 6 isn't from a x-wing.
instead its from the xy-wing present in this image
in
r1c2 {2,4}
r3c1 {4,6}
r3c5 {2,6}



the xy-wing says that either the 2 in r1c2 is true,
or
the 2 in r3c5 is true,
no matter which direction through the chain you go.

this eliminates the 2 in r1c6 and places 6 in that cell.


thank you for help- and that makes sense on the surface- but if you can answer two questions I think I might "get it":
1) why doesn't the "wing" go the other direction, with the {2,6} in r1c6 instead of the one in r3c5?
2) if the xy wing we're concerned about involves 2,4,6 why doesn't the {2,4} in r3c9 figure into the thinking?

thanks again for the direction.
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Marty R.



Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA
PostPosted: Sun May 03, 2009 3:39 pm    Post subject: Reply with quote
Quote:
1) why doesn't the "wing" go the other direction, with the {2,6} in r1c6 instead of the one in r3c5?
2) if the xy wing we're concerned about involves 2,4,6 why doesn't the {2,4} in r3c9 figure into the thinking?


As to question #1, there are two wings available. The pivot (the XY cell) could be 46 in r3c1 or 24 in r1c2. Both accomplish the same.

The 24 in r3c9 isn't part of a wing, it's part of a naked triple (all three cells in the same house.)
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wapati



Joined: 10 Jun 2008
Posts: 472
Location: Brampton, Ontario, Canada.
PostPosted: Sun May 03, 2009 4:47 pm    Post subject: Reply with quote
If you want to use the 24 pair in r3c9 it is part of a w-wing.
Code:
.---------------------.---------------------.---------------------.
| 5     *24     2369  | 1      7     #26    | 8      239-4  23-4  |
| 39     7      239   | 4      8      5     | 6      239    1     |
| 6-4    8      1     | 9     #26     3     | 7      5     *24    |
:---------------------+---------------------+---------------------:
| 34     45     7     | 2      9      14    | 135    8      6     |
| 3469   245    2369  | 8      456    146   | 12359  2349   7     |
| 8      1      269   | 56     3      7     | 259    249    245   |
:---------------------+---------------------+---------------------:
| 2      6      5     | 3      1      9     | 4      7      8     |
| 7      9      4     | 56     256    8     | 235    1      235   |
| 1      3      8     | 7      245    24    | 25     6      9     |
'---------------------'---------------------'---------------------'


Of the cells marked with "#", one of them must be a 2.
That means that one of the cells marked with "*" must be a 4.

The cells that see both of the ones marked with "*" cannot be a 4.
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